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BMC Ecology BioMed Central Research article Open Access Preliminary inventory and classification of indigenous afromontane forests on the Blyde River Canyon Nature Reserve, Mpumalanga, South Africa Mervyn C Lötter*1 and Hans T Beck*2 Address: 1Terrestrial Services, Scientific Services, Mpumalanga Parks Board, Private Bag X1088, Lydenburg, 1120, South Africa and 2Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115 USA Email: Mervyn C Lötter* - [email protected]; Hans T Beck* - [email protected] * Corresponding authors Published: 02 August 2004 Received: 31 January 2004 Accepted: 02 August 2004 BMC Ecology 2004, 4:9 doi:10.1186/1472-6785-4-9 This article is available from: http://www.biomedcentral.com/1472-6785/4/9 © 2004 Lötter and Beck; licensee BioMed Central Ltd. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Mixed evergreen forests form the smallest, most widely distributed and fragmented biome in southern Africa. Within South Africa, 44% of this vegetation type has been transformed. Afromontane forest only covers 0.56 % of South Africa, yet it contains 5.35% of South Africa's plant species. Prior to this investigation of the indigenous forests on the Blyde River Canyon Nature Reserve (BRCNR), very little was known about the size, floristic composition and conservation status of the forest biome conserved within the reserve. We report here an inventory of the forest size, fragmentation, species composition and the basic floristic communities along environmental gradients. Results: A total of 2111 ha of forest occurs on Blyde River Canyon Nature Reserve. The forest is fragmented, with a total of 60 forest patches recorded, varying from 0.21 ha to 567 ha in size. On average, patch size was 23 ha. Two forest communities – high altitude moist afromontane forest and low altitude dry afromontane forest – are identified. Sub-communities are recognized based on canopy development and slope, respectively. An altitudinal gradient accounts for most of the variation within the forest communities. Conclusion: BRCNR has a fragmented network of small forest patches that together make up 7.3% of the reserve's surface area. These forest patches host a variety of forest-dependent trees, including some species considered rare, insufficiently known, or listed under the Red Data List of South African Plants. The fragmented nature of the relatively small forest patches accentuates the need for careful fire management and stringent alien plant control. Background 0.56 % of South Africa [3], yet it contains 5.35% of South Mixed evergreen forests form the smallest, most widely Africa's plant species [4]. These forests have a relatively distributed and fragmented biome in southern Africa [1]. high species richness of 0.58 species km-2, exceeding the Originally classified as Undifferentiated Afromontane for- grassland biome with 0.25 species km-2 and lagging only est [2], 44% of this vegetation type within South Africa the fynbos with 1.36 species km-2[5]. The forest biome has been transformed [2]. The forest biome only covers occurring in Mpumalanga is now recognized as Page 1 of 11 (page number not for citation purposes) BMC Ecology 2004, 4:9 http://www.biomedcentral.com/1472-6785/4/9 Mpumalanga Mistbelt Forest [6], and it covers only 0.51% Results of the province's surface area [7]. Cooper [8] conducted a Spatial distribution of forests study on the conservation status of indigenous forests We found a total area of 2111 ha of afromontane forest on within Transvaal, Natal and the Orange Free State, in BRCNR. This comprises 7.3% of the reserve's total surface which he estimated the Blyde River Canyon Nature area. Figure 2 shows the distribution of the forest on Reserve's (BRCNR) forests at 352 ha. Recently, ownership BRCNR. The forest is fragmented, with a total of 60 forest of a 700 ha forest tract bordering on BRCNR at the base of patches recorded, varying from 0.21 ha to 567 ha in size. the Drakensberg Escarpment was transferred to the Mpu- The number of patches per size class illustrates this level malanga Parks Board (MPB). Therefore, it was thought of fragmentation (Figure 3). Unfortunately, 15 % of the that just over 1000 ha of forest occurred on BRCNR. larger forest patches have their patch size delimited by political boundaries. This means that a few forest patches To begin to understand the nature and distribution of for- continued over BRCNR's borders onto adjacent land and ests in the BRCNR landscape, we need to have an accurate only the portions occurring on BRCNR were included in surface area inventory, a species composition list, and an the calculations. If the average patch size is only calculated identification and classification of the communities. from patches with natural boundaries within the reserve, Standard ecological fieldwork coupled with remotely then the average size of forest patches is only 23 ha. This sensed data and GIS allow for an efficient analysis. Prior small patch size accentuates the fragmented nature of the to this investigation of the indigenous forests on BRCNR afromontane forest on BRCNR. very little was known about the size and floristic compo- sition of the forest biome conserved within the reserve. In Flora and forest classification comparison, the grassland biome has received much The forest flora recorded in 22 relevés is listed in Appendix attention on BRCNR with a monitoring program set up to A (see additional file 1). The total of 167 species includes assess the status of the grasslands. We report here an 38 ferns and fern allies, 3 conifers and 140 flowering inventory of forest size, fragmentation, species composi- plants (11 monocots, 131 dicots). Previous botanical field tion and the basic floristic communities along environ- work and logistical reconnaissance of the forest fragments mental gradients. within the park boundaries showed the forest flora to be qualitatively similar. However, some areas of the frag- Study area ments were unreachable or technically difficult to visit BRCNR is situated on the northern Drakensberg Escarp- and study due to the escarpment topography. For pur- ment, Mpumalanga Province, South Africa (24°40'S lon- poses of this vegetation analysis, the relevés were located gitude, 30°51'E latitude; Figure 1). The Mpumalanga (Figure 4) in two of the five largest forest patches, located Parks Board administers this reserve, which is approxi- in the central region of the BRCNR, where forest frag- mately 29 000 ha in size. The elevation on BRCNR ranges ments were at least reasonably accessible. At this time, we from 560 m to 1944 m above sea level. The stratigraphy of consider these relevés to be representative. While the for- the northern Drakensberg Escarpment region is com- est flora of BRCNR has not been exhaustively surveyed, posed of sediment rock types (quartzite, shale, and dolo- this species list represents our best knowledge collected to mite) of the Transvaal Supergroup [9], dominated by date. Black Reef Quartzite and Wolkberg Group [10]. Rainfall varies from 541 mm to 2776 mm per annum. Variation in From our analysis of the forest vegetation in the relevés, altitude and rainfall, associated with a landscape of geo- two main plant communities – moist afromontane forest logical and pedological extremes, has created a very at high altitude and dry afromontane forest at lower alti- diverse flora. The landscape is prone to lightning-induced tude – are identified and described below. An eigenvalue burning [11] and is topographically complex, hosting a of 0.33 was produced from the TWINSPAN algorithm at variety of habitats [12], including grassland plateaus, wet- the first division into two communities. This value is lands and sponge areas, grassland slopes, afromontane strong enough to represent beta diversity and the division forest, riparian forest, moist woodlands, dry woodlands into two plant communities is accepted. Each community and shrublands. The vegetation type is classified as the was then further broken down again into two communi- Northeastern Drakensburg High-Mountain Sourveld ties, whose eigenvalues were lower and therefore taken as ecoregion [13], and the reserve encompasses four veld a measure of alpha diversity. The four proposed sub-com- types: Afromontane Forest, North-eastern Mountain Sour munities are accepted as variants within the two larger Grassland, Sour Lowveld Bushveld, and Mixed Lowveld communities. A complimentary analysis of forest com- Bushveld [14]. munities using DECORANA was carried out and supports the results of the CANOCO analysis. Figure 5 displays the results from the CANOCO analysis. This joint plot data is analyzed for relationships with environmental data. These Page 2 of 11 (page number not for citation purposes) BMC Ecology 2004, 4:9 http://www.biomedcentral.com/1472-6785/4/9 ReserveFigure 1location Reserve location. The Blyde River Canyon Nature Reserve is located in northeastern Mpumalanga Province, South Africa. Page 3 of 11 (page number not for citation purposes) BMC Ecology 2004, 4:9 http://www.biomedcentral.com/1472-6785/4/9 ForestFigure distribution 2 Forest distribution. Distribution of afromontane forest fragments in the Blyde River Canyon Nature Reserve. Page 4 of 11 (page number not for citation purposes) BMC Ecology 2004, 4:9 http://www.biomedcentral.com/1472-6785/4/9 Degraded moist high-altitude forest Forest Patches per Size Class A very broken and open canopy with a large shrub com- in Blyde River Canyon Nature Reserve ponent characterizes this forest type. A number of species within this community are shade-intolerant and have 25 23 established themselves under an open canopy. This sub- 21 community has been so over-utilized that the canopy has 20 never been able to close and this community is sometimes dominated by the exotic invader species Acacia mearnsii.